Experimental measurements of nitrogen remineralization in coastal waters 1

Ammonium remineralization was measured in the euphotic zone of two coastal areas using a 15 N isotope dilution technique. Remineralization fluxes were high in both areas and often exceeded assimilation fluxes. A strong positive correlation between ammonium remineralization and ammonium and carbon dioxide assimilation suggests a close coupling of photosynthesis and nitrogen recycling. Regenerative fluxes decreased with depth and with distance offshore, but to a relatively lesser extent than did assimilative fluxes. Turnover times for remineralzation of utilizable organic nitrogen were estimated to be from 3 to 16 clays. Size fractionation experiments and estimates from the literature suggest that microplankton (<183 µ cm) may have been the primary nitrogen remineralizers.